Subunit composition of lipoprotein(a) protein

Area of Science:

• Biochemistry
• Lipid Metabolism
• Molecular Biology

Background:

• Lipoprotein(a) (Lp(a)) is a lipoprotein particle implicated in cardiovascular disease.
• The composition of Lp(a), specifically the ratio of its apolipoprotein components, is crucial for understanding its function and pathogenicity.
• Apolipoprotein(a) (apo(a)) exhibits significant structural heterogeneity due to variable numbers of kringle 4 domains.

Purpose of the Study:

• To determine the molecular weight of different apolipoprotein(a) (apo(a)) polymorphs.
• To estimate the molar ratio of apo(a) to apolipoprotein B (apoB) within Lp(a) particles.
• To elucidate the stoichiometry of apo(a) and apoB in Lp(a) using physicochemical methods.

Main Methods:

• Sedimentation equilibrium ultracentrifugation in 6 M guanidine hydrochloride was employed to determine molecular weights.
• Analysis of Lp(a) particle mass, apo(a) mass after reduction and carboxymethylation, and lipid-free apoB-apo(a) complex mass were utilized.
• Carbohydrate content and partial specific volume of apo(a) polymorphs were measured.

Main Results:

• Four apo(a) polymorphs with molecular weights of 289,000, 310,000, 341,000, and 488,000 were identified, corresponding to 15, 16, 18, and 27 kringle 4 domains, respectively.
• Carbohydrate content (23.2 wt %) and partial specific volume (0.682 mL/g) were consistent across polymorphs.
• Multiple physicochemical methods consistently indicated a stoichiometry of two apo(a) molecules to one apoB molecule in the investigated Lp(a) particles.

Conclusions:

• The protein moiety of Lp(a) particles comprises a complex of two apo(a) molecules and one apoB molecule.
• This stoichiometric finding provides critical insights into the structural basis of Lp(a) heterogeneity.
• Understanding Lp(a) composition is essential for further research into its atherogenic potential and therapeutic targeting.